Synthesis and Thermophysical Properties of Ether-Functionalized Sulfonium Ionic Liquids as Potential Electrolytes for Electrochemical Applications

Article abstract of DOI:10.1002/cphc.201600882

During this work, a novel series of hydrophobic room temperature ionic liquids (ILs) based on five ether functionalized sulfonium cations bearing the bis{(trifluoromethyl)sulfonyl}imide, [NTf₂]^? anion were synthesized and characterized. Their physicochemical properties, such as density, viscosity and ionic conductivity, electrochemical window, along with thermal properties including phase transition behavior and decomposition temperature, have been measured. All of these ILs showed large liquid range temperature, low viscosity, and good conductivity. Additionally, by combining DFT calculations along with electrochemical characterization it appears that these novel ILs show good electrochemical stability windows, suitable for the potential application as electrolyte materials in electrochemical energy storage devices.

Full text of DOI:10.1002/cphc.201600882

Accepted Article
Title: Synthesis and Thermophysical Properties of Ether Functionalized Sulfonium
Ionic Liquids as Potential Electrolytes for Electrochemical Applications
Authors: Erwan Coadou; Peter Goodrich; Alex R. Neale; Laure Timperman; Chri-
stopher Hardacre; Johan Jacquemin; M e´ ri e` m Anouti
This manuscript has been accepted after peer review and the authors have elected
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of the final Version of Record (VoR). This work is currently citable by using the Digital
Object Identifier (DOI) given below. The VoR will be published online in Early View as
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To be cited as: ChemPhysChem 10.1002/cphc.201600882
Link to VoR: http://dx.doi.org/10.1002/cphc.201600882
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
Synthesis and Thermophysical Properties of Ether Functionalized
Sulfonium Ionic Liquids as Potential Electrolytes for
Electrochemical Applications
,
[a],[b]
[a]
[a]
[b]
[a],[c]
Erwan Coadou,*
Peter Goodrich, Alex R. Neale, Laure Timperman, Christopher Hardacre,
,
[a]
[b]
Johan Jacquemin,* and Mérièm Anouti
Abstract: During this work, a novel series of hydrophobic room
applications. To date, however, most of these ILs have been
[
7]
[8]
[9]
temperature ionic liquids (ILs) based on five ether functionalized
based on imidazolium, tetraalkylammonium, pyridinium, and
[
10]
sulfonium cations bearing the bis{(trifluoromethyl)sulfonyl}imide,
quaternary phosphonium cations.
Despite having a lower
-
[
NTf
2
]
anion were synthesized and characterized. Their
viscosity, higher conductivity and lower melting points; ILs based
on trialkylsulfonium cations have attracted limited attention
physicochemical properties, such as density, viscosity and ionic
conductivity, electrochemical window along with thermal properties
including phase transition behavior and decomposition temperature,
have been measured. All of these ILs showed large liquid range
temperature, low viscosity and good conductivity. Additionally, by
[
11]
compared to their ammonium and phosphonium analogues
[12]
with other research groups emphasizing the use of cyclic and
[13]
acyclic sulfonium ILs
as electrolytes for energy devices.
Recently, we also reported the use of protic and aprotic
sulfonium ILs as potential electrolytes for electric double-layer
combining
DFT
calculations along
with
electrochemical
[14]
characterization it appears that these novel ILs show good
electrochemical stability windows, suitable for the potential
application as electrolyte materials in electrochemical energy
storage devices.
capacitors (EDLC) devices.
In addition, numerous publications have highlighted the
influence of the presence of an ether functionalization on the
[
15]
physiochemical properties of acyclic ammonium-based
cyclic ammonium-based ILs.
and
Research surrounding the
influence of mono-ether functionalization on the properties of
[
16]
[
17]
sulfonium-based ILs has only been studied by Han et al. and
1. Introduction
[18]
Orita et al.
In this paper, we extended this family of
hydrophobic room temperature ILs based on mono-ether and
diether containing alkyl chains appended to sulfonium cations.
These ether containing chains are of particular interest for
energy storage systems such as supercapacitors and Li
batteries due to the possible improved transport properties and
good electrochemical stability. Furthermore, the ethereal groups
may also offer to the Li cation migrating through the bulk solution
in the case of electrolyte for Li batteries, for example. The
investigation of viscosity, density, thermal phase behavior,
thermal stability, electrochemical stability and ionic conductivity
were undertaken. Finally, ILs electrochemical stability results
were also analyzed in combination with DFT calculations to
further understand the effect of the ether functionalization in the
cation on this property.
Ionic liquids (ILs) have gained considerable interest over the
past few decades due to their numerous attractive properties
such as extremely low vapor pressure, low flammability, high
thermal stability and large liquid range. This has led to a number
of groups researching IL applications particularly in the fields of
[
1]
[2]
catalysis, and separations. In comparison with molecular
solvents, ILs also possess high ionic conductivity coupled with
good electrochemical stability and, therefore, have been touted
[3]
as new electrolytes for energy devices such as solar cells, fuel
[
4]
[5]
[6]
cells, lithium batteries, and supercapacitors.
Within the fields of lithium batteries and capacitors a number of
various ILs have been developed with specific physiochemical
[
a]
Dr. E. Coadou, Dr. P. Goodrich, Mr. A.R. Neale, Prof. C. Hardacre,
Dr. J. Jacquemin*
2. Results and Discussion
The QUILL Research Centre, School of Chemistry and Chemical
Engineering
Queen’s University of Belfast
2.1. Synthesis of the sulfonium ILs
Stranmillis Road, Belfast BT9 5AG, United Kingdom
E-mail: johan.jacquemin@qub.ac.uk
Dr. E. Coadou, Dr. L. Timperman, Prof. M. Anouti
Laboratoire PCM2E
The general synthesis method of the selected sulfonium based
[
SR ][NTf ] ILs is described in the experimental section. The
3
2
[
b]
c]
various ether and alkyl substituents R attached to the sulfonium
center are listed in Table 1 and the ILs and intermediates (1a,
Université François Rabelais
Parc de Grandmont 37200 Tours, France
E-mail: erwan.coadou@etu.univ-tours.fr
Prof. C. Hardacre
School of Chemical Engineering & Analytical Science
The University of Manchester
1b, 2a and 2b) are shown in Figure 1. Several synthetic
strategies were undertaken to develop these ILs with the
maximum yield and purity. Initial attempts to synthesis these
materials using conventional procedures employed for
imidazolium- or ammonium-based ILs proved problematic due to
the lower alkylation yield observed between the sulfide and the
[
The Mill, Sackville Street, Manchester, M13 9PL, United Kingdom
Supporting information for this article is given via a link at the end of
the document
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
[
19]
ethers, as shown in Figure 1, route 1.
Therein, low to
For lab-scale synthesis of these ether-functionalised ILs, the
commercial availability and good reactivity of 1-bromo-2-(2-
methoxyethoxy)ethane and 2-bromoethyl methyl ether, make
them attractive reagents for relatively straightforward alkylation.
However, for larger scale preparation, the bromide containing
groups become less feasible. In this context, alternative
synthetic strategies wherein alkoxy functionalization is
completed using less toxic reagents, (e.g. sulfonate esters,
tosylates) have been described in literature and, furthermore,
moderate yields of deeply colored ILs were obtained. Therefore,
the proposed strategy was to firstly synthesize the
corresponding thioethers 1a and 1b and if possible alkylate at
the final step. These thioethers 1a and 1b were easily
synthesized using the conventional Williamson procedure under
[
20]
aqueous conditions.
The corresponding alkylation of the
thioethers using either iodomethane or diethylsulfate, via route 2
in Figure 1 also proceeded smoothly to yield the corresponding
dialkylether-sulfonium ILs.
[
21]
reviewed in depth.
Alkylation of the thioethers 1a and 1b with other bromoethers to
form the alkyldiether sulfonium ILs proved to be more difficult
due decreases in nucleophilicity of the sulfur center resulting in
lower yields of the desired ILs, see route 3 in Figure 1. Therefore,
Table 1. Abbreviations and alkyl side chains of the sulfonium cations
[SR ] .
3
+
a
different synthetic strategy was adopted to produce
alkyldiether-sulfonium ILs, as shown in Figure 1, route 4.
Therein, sodium sulfide was reacted with 2 equivalents of the
corresponding bromogylme to form thiodiethers 2a and 2b.
Alkylation of these thioethers with iodomethane proceeded
1
2
3
Abbreviation
R
R
R
[
S
1,1,G1][NTf
[S1,1,G2][NTf
1,2,G1][NTf
2
]
2
]
2
]
CH
CH
CH
3
3
3
CH
CH
CH
3
3
2
CH
(CH
CH
CH CH OCH
2
CH
CH
CH
2
OCH
O) CH
OCH
3
smoothly to furnish the alkyldiether sulfonium iodide which
2
2
2
3
-
underwent metathesis to form the corresponding [NTf
2
] -based IL.
[S
CH
3
2
2
3
The metathesis anion exchange reactions were completed in
-
ultrapure water, yielding biphasic systems wherein the [NTf
2
] -
[S1,G1,G1][NTf2]
CH3
CH
2 2
CH CH OCH
3
2
2
3
based ILs occupied the bottom, non-aqueous phase.
Undertaking these new synthetic strategies produced colorless
ILs in 63-87 % isolated yield (see experimental section and
Figures S1-S5 of the Electronic Supplementary Information
[S
1,G2,G2][NTf
2
]
3
(CH
2
CH
2
O)
2
CH
3
(CH
2
CH
O) CH
2 2 3
(
ESI)).
Figure 1. Strategic routes for the synthesis of sulfonium ether ILs.
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
-
2
Table 2. Density, transport and thermal properties of the selected [NTf ] -based sulfonium ILs at atmospheric pressure.
[
a]
[a]
[a]
Mw
g·mol )
T
m
T
f
T
g
ρ
η
σ
T
d
Cation
-1
-3
-1
(
(K)
(K)
(K)
(g·cm )
(mPa·s)
(mS·cm )
(K)
+
+
+
[S
[S
[S
[S
[S
1,1,G1
1,1,G2
1,2,G1
]
]
]
401.37
445.42
415.39
445.42
533.52
267.54
223.43
189.23
194.61
215.15
1.5229
1.4689
1.4814
1.4638
1.3883
46.84
33.10
30.84
27.67
35.86
3.94
2.85
4.93
3.87
2.34
512
505
517
512
492
-
-
-
-
-
-
-
-
+
+
[b]
1,G1,G1
1,G2,G2
]
<183
]
194.94
[
a], recalculated at 298.15 K using fitting equations (see below). [b], not detectable.
2
.2. Physical characterization of the sulfonium ILs
less thermally stable than their analogous non-functionalized ILs
primarily due to the weakened cation–anion electrostatic
interaction freeing the anions to act as nucleophiles. For
The thermal properties of selected ILs were characterized by
differential scanning calorimetry (DSC) and thermal gravimetric
analysis (TGA). Furthermore, the density (), dynamic viscosity
example, [S1,1,G1][NTf
lower than the analogous non-functionalized [S1,1,4][NTf
Increasing the carbon chain from methyl [S1,1,G1][NTf ] (Figure
S6a of the ESI) to ethyl [S1,2,G1][NTf ] (Figure S6c of the ESI)
resulted in a slight increase in T . The addition of more ether
units G (Figures S6b and S6e of the ESI) vs. G (Figures S6a
2 d
] (Figure S6a of the ESI) had a T ≈ 38 K
[23]
2
] IL.
(
) and ionic conductivity () were determined as the function of
2
temperature at atmospheric pressure. This characterization data
is summarized in Table 2.
2
d
2.2.1. Thermal properties
2
1
The thermal behavior of the studied ILs was investigated by
DSC from 183.13 K to 373.15 K. As shown in Figure S6 (left) of
and S6d of the ESI) resulted in a slight lowering of the
decomposition temperature. Despite this lowering of the
the ESI, most of the ILs only exhibited glass transitions, T
only the [S1,1,G1][NTf ] functionalized IL showing an observable
melting transition, T
g
, with
decomposition temperature, the T
higher than those temperatures (373-398 K) encountered in high
temperature energy storage devices. Additionally, as depicted
from the Figure S6 of the ESI and Table 2, all investigated ILs
have a large liquid range temperature, which is higher than 240
d
values are still significantly
2
[
27]
m
, at 267.54 K and freezing transition, T
f
, at
2
23.43 K. This supercooling phenomenon has been previously
[
22]
well documented for imidazolium- and ammonium-based ILs.
Interestingly, the analogous non-functionalized [S1,1,4][NTf
2
[18]
] was
2
K in the case of the [S1,1,G1][NTf ] and exceeds 300 K for the
[
23]
observed to have a T
m
between 269.55 K and 271.55 K as
other ILs. In fact, each IL may be potentially used as electrolytes
in low (e.g. 268 K) and/or high (e.g. 473 K) temperatures energy
storage devices.
measured by two independent research groups. Although we
are only comparing one set of ILs, generally, reports in the
literature suggest that functionalization of IL alkyl chains with
ether groups results in a decrease in melting and increase in
2.2.2. Physico-chemical properties of selected ILs
The fundamental properties of the sulfonium ILs, including
physicochemical quantities of density (), viscosity (),
conductivity (), and their iconicity have been investigated as
detailed below.
[
24]
liquid range.
functionalization with either G
Figures S6b and S6e of the ESI) did result in a significant
increase in liquid range. Furthermore, by increasing the alkyl
chain length from C (Figure S6a of the ESI) to C in (Figure S6c
Within the ILs studied, increased ether
1
(Figure S6d of the ESI) or with G
2
(
−3
The densities ( / g·cm ) have been measured from 293.15 K to
1
2
363.15 K at atmospheric pressure for all the investigated ILs
of the ESI) also led to an increase in the liquid range
temperature. Therein, the most plausible explanation for the
(
2
see tabulated data in Table S1 of the ESI). As shown in Figure
−3
, the density of selected sulfonium ILs are between 1.38 g·cm
observed lack of T
m
is due to the increased rotational freedom
−3
and 1.53 g·cm at 298.15 K, values which are in line with other
sulfonium
and subsequent reduction in lattice energy as has been
-
[23,28]
[NTf
2
] -based
ILs
previously
reported.
[
25]
described elsewhere.
with regards to the IL functionalization. In addition, as evidenced
from the transport studies, the low T values observed do not
always lead to low fluidities due to fragility.
g
The T values showed no correlation
Furthermore, the density decreases with temperature as
expected. Generally, and as shown in Figure 2, over a narrow
range of temperatures, the temperature dependence on the
density can be expressed as follows:
g
[26]
To further investigate the thermal properties of the selected
sulfonium-based ILs, TGA analysis of each sample has been
carried-out. As shown in Figure S6 (right) of the ESI, the
= a + b·T
(1)
where a, b are the fitting parameters and T is the temperature in
Kelvin.
d
decomposition temperatures, T , of these sulfonium ILs are in
2
the range of 492.15 - 517.15 K, significantly lower (< 150 K) than
Within the ILs studied a strong linear relationship (R > 0.9999)
[
22b]
that observed for analogous ammonium-based ILs.
In
with temperature was obtained and the best fitting parameters of
eq. (1) are summarized in Table S2 of the ESI. Furthermore, as
addition, the short-chain-ether functionalized ILs tended to be
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
shown in Figure 2, the density of the ILs decreases by
increasing the degree of functionalization within the alkyl chain
This is, however, somewhat higher than the corresponding
-
bis(fluorosulfonyl)imide [FSI] anion which was reported to have
+
+
+
+
.
[17]
and follows the trend, [S1,1,G1] > [S1,2,G1] > [S1,1,G2] > [S1,G1,G1
]
a viscosity of 30.0 mPa s at 298.15 K.
This decrease in
+
>
[S1,G2,G2] . As the density is governed by the cation-anion
viscosity upon the addition of ether units into the alkyl chain is
not surprising given the decrease in van der Waals interactions
[29]
interaction and molecular packing,
which reduces with
[
33]
increasing ether functionalization and/or increase in alkyl chain,
this trend mirrors those already reported in the case of the ether
and has also been reported for other ether functionalized ILs.
In addition, all of the ILs showed comparable or significantly
lower viscosities than the corresponding mono-ether containing
[30]
functionalized imidazolium-based ILs.
[
24b]
.
[34]
pyrrolidinium
(53 mPa s at 298.15 K), piperidinium
(55
.
[35]
.
mPa s at 298.15 K), linear guandinium (58 mPa s at 298.15 K)
and cyclic guandinium
[
35]
.
(46 mPa s at 298.15 K). More
surprising, was the similar viscosities observed for the remaining
ILs regardless of the degree of ether functionalization. In this
regard, negligible differences in viscosity have been reported for
[
36]
di- and triether based imidazolium acetate ILs
analogous di- and trialkyl ammonium acetate based ILs.
and the
[
37]
Figure 2. Temperature dependence on the density of
[
[
S
1,1,G1][NTf
2
]
(), [S1,1,G2][NTf
] () and [S1,G2,G2][NTf
2
]
(), [S1,2,G1][NTf
] () at 0.1 MPa. The lines
2
]
(),
S1,G1,G1][NTf
2
2
represent the linear regression of each density dataset using
parameters reported in Table S2 of the ESI.
The viscosity ( / mPa·s) is also an important property for
assessing ILs with respect to their use as electrolyte media in
energy devices, because of the strong association of the rate of
mass transport. The electrolytes in many energy devices are
required to operate at near ambient temperature ranges. In other
words, any IL used as an electrolyte should have a low viscosity
particularly at room temperature. Currently, one of the largest
barriers for the application of the ILs as pure electrolytes is their
high viscosity in comparison with classical electrolytes for either
Figure 3. Viscosity of the sulfonium-based ILs: [S1,1,G1][NTf
] (), [S1,2,G1][NTf ] (), [S1,G1,G1][NTf ] () and
[S1,G2,G2][NTf ] () as the function of temperature from 267 K to
370 K at 0.1 MPa. The solid lines correspond to the VTF-type
fitting equations with parameters reported in Table S5 of the ESI.
2
] (),
[S1,1,G2][NTf
2
2
2
2
The conductivity of an IL is also of vital importance if it is to be
considered as a supporting electrolyte in energy devices.
Generally, the ionic conductivity of ILs is mainly governed by
-1
-3
supercapacitors (55 mS·cm at 0.6 mPa·s for 1 mol·dm
[
31]
[
Et
4
N][BF
4
] in acetonitrile at 298.15 K)
or Li batteries (9.7
-
1
-3
[38]
mS·cm at 0.5 mPa·s for 1 mol·dm Li[PF
carbonate:dimethylcarbonate blend at 298.15 K).
6
] in ethylene
their viscosity, formula weight, density and ion size. As shown
[
32]
In this
in Figure 4, the conductivity of the ILs increases with increasing
temperature, as expected. Furthermore, the ionic conductivity of
regard, the investigated sulfonium-based ILs show viscosities
ranging from 28 to 53 mPa·s at 298.15 K (see Table S3 of the
ESI). As shown in Figure 3, the viscosity of the ILs decreases
with increasing the temperature, as expected. Furthermore, the
viscosity seems to be strongly affected by the size and the
symmetricity of the cation as well as by the degree of
functionalization within the alkyl chain and follows the trend:
+
+
the ILs decreases with the following trend, [S1,2,G1] > [S1,1,G1] >
+
+
+
[S1,G1,G1] > [S1,1,G2] > [S1,G2,G2] and covers the range of 2.3-5.0
-
1
-1
mS·cm and of 10.8-20.2 mS·cm at 298.15 K and 353.15 K,
respectively (see Table S4 of the ESI).
The small difference in ionic conductivity data even at the lower
temperatures suggests that the transport of the ions in these
sulfonium ILs is perhaps more dependent on their viscosity.
+
+
+
+
+
[S1,1,G1] > [S1,G2,G2] > [S1,1,G2] > [S1,2,G1] > [S1,G1,G1] .
To the best of our knowledge the viscosity of the [S1,G1,G1][NTf
2
]
Conversely, for example at 298.15 K, the [S1,1,G1][NTf
2
] and
IL (27.67 mPa·s at 298.15 K) is the lowest of any reported ether
[S1,2,G1][NTf
2
] ILs show significantly lower ionic conductivities
-
-1
functionalized [NTf
] (46.84 mPa·s at 298.15 K) is slightly lower than
that of the analogous non-functionalized sulfonium IL, such as
2
] IL, to date. Even the most viscous IL, i.e.
(3.94 and 4.93 mS·cm ) compared to the analogous
corresponding ILs with the [FSI] anion (9.5 and 7.6 mS·cm ,
respectively), although they have comparable viscosities. This
also clearly indicates that an IL containing a common cation and
-
-1
[
S
1,1,G1][NTf
2
[
17]
[
18]
2
the [S1,1,4][NTf ] (63.0 mPa·s at 298.15 K) previously reported.
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
an anion with a lower molecular weight and smaller size is also
more favorable for the production of more conductive salts.
temperature are reported in the Table S5 of the ESI, together
with correlation coefficient R for the fit.
2
When comparing the ideal glass-transition temperatures derived
from VTF-type fitting (i.e. T values in the Table S5 of the ESI)
0
using the ionic conductivity and viscosity measurements, it can
be seen that the corresponding values for each IL show good
correlations (i.e. < 10 %) except in the case of the [S1,G2,G2][NTf
i.e. ≈ 22 %). Nevertheless, irrespective of the IL examined, no
trend can be observed between T and T values from both VTF-
type fittings. With the exception of [S1,G2,G2][NTf ], all of the ILs
significantly lower than those obtained for the
2
]
(
g
0
2
show theoretical T
0
[
40]
DSC derived T
g
highlighting the fragile nature of these ILs.
The Arrhenius activation energies for both viscosity and
conductivity are also depicted in Table S5 of the ESI, and are
calculated between the temperature range 293.15 and 353.15 K.
As expected, for each IL the activation energy for conductivity is
[
41]
lower than that for viscosity due to the fractional Walden rule.
Unlike the Arrhenius equation, all VTF equations seem to
correlate accurately each property over a wider temperature
range allowing better predictions for both the limiting viscosity
Figure 4. Ionic conductivity of the sulfonium-based ILs
[
[
S
1,1,G1][NTf
2
]
(), [S1,1,G2][NTf
] () and [S1,G2,G2][NTf
2
]
(), [S1,2,G1][NTf
2
]
(),
S1,G1,G1][NTf
2
2
] () as the function of
(

0 0
) and limiting conductivity ( ), see Table S5 of the ESI. This
temperature from 263.15 K to 353.15 K at 0.1 MPa. The solid
lines correspond to the VTF-type fitting equations with
parameters reported in Table S5 of the ESI.
correlation allows better determination of the Walden ionicity of
the selected ILs as a function structure and temperature. Prior to
constructing the Walden plot, the molar conductivity (
S·cm ·mol ) data must be calculated within the same
m
/
2
-1
2
The [S1,G2,G2][NTf ] IL also showed the smallest ionic conductivity
temperature range for each IL according to eq. 4.
-1
(
(
at 298.15 K,  = 2.34 mS·cm ), despite having a lower viscosity
at 298.15 K,  = 35.86 mPa·s) than the [S1,1,G1][NTf ] (at 298.15
2
ꢓꢔ
-1
ꢐꢑ ꢀꢈꢒ
ꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇ(ꢖ)
K,  = 46.84 mPa·s and  = 3.94 mS·cm ). In this regard, the
distinction must be made between these two transport properties.
The viscosity measured experimentally is macroscopic in nature,
which is clearly related to the cohesive energy of the solution;
whereas the conductivity of selected sulfonium-based ILs seems
to be more strongly affected by the structure (volume),
interaction (packing) and then the mobility of ions in the solution.
One way to investigate the relationship between the viscosity
ꢕ
-1
-1
−3
where,  (S·cm ), Mw (g·mol ) and  (g·cm ) are the ionic
conductivity, the molecular weight and the density of the
selected ILs.
2
-1
The Walden plot (i.e. the variation of log10(
m
/ S·cm ·mol ) vs.
log10(1/ / P )) for the five neat ILs within a temperature range of
93.15 K to 353.15 K is presented in Figure 5. The specific
-1
2
(
fluidity) and the conductivity (resistivity) of selected sulfonium-
points on the graph were calculated using the correlation
parameters of the fitting equations for density (eq. 1 with
parameters reported in Table S2 of the ESI), conductivity, and
viscosity (eq. 3 with parameters reported in Table S5 of the ESI)
from 293.15 K to 353.15 K within steps of 10 K. The solid line in
Figure 5 represents a so-called ideal KCl line, i.e. the ideal
based ILs is driven by the determination of their ionicity thanks
[
26]
to the utilization of the Walden plot.
Prior to investigation of
the effect of the temperature on the ionicity of the studied ILs,
each property has to be correlated as the function of the
temperature.
Herein, as shown in Table S5 of the ESI, all of these ILs
deviated slightly from the Arrhenius behavior (eq. 2) but could be
better described by the Vogel-Tamman-Fulcher (VTF) type
equation (eq. 3). This is not a surprising result as many other ILs
-3
Walden behavior of a 0.01 mol∙dm aqueous solution of KCl, a
strong electrolyte, where the constituent ions are known to be
[
42]
fully dissociated and equally mobile in solution. As shown in
Figure 5, a deviation below this ideal line is observed for all
investigated sulfonium-based ILs, which may indicate, in each
case, that not all ionic species are available for the conduction of
charge and their apparent electrolytic conductivity is lower than
may be expected for a given viscosity. In other words, this may
be related to a slight tendency for the formation of ion pairs in
[
39]
are generally well described by the VTF equation.
ꢄ
ꢋ
ꢂꢃ
ꢂ
ꢃ
ꢀ
ꢀ
ꢁ[
]ꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢈꢀꢈ ꢉꢊ
ꢌꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇ(ꢍ)
ꢌꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇ(ꢏ)
ꢁ
(
ꢅꢆ)
(ꢅꢆ)
ꢎꢄ
ꢎꢋ
(ꢆꢊꢆꢁ)
ꢁꢉ
ꢌꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢈꢀꢈ ꢉꢊ
each IL. This is not a surprising result as such behavior has
ꢁ
(
ꢆꢊꢆꢁ)
[43]
been reported for several ILs.
Furthermore, as reported in
Table S6 of the ESI, by applying the “classical” Walden rule, it
appears clearly that the corresponding Walden product, W =
-1
where 
K) are the Arrhenius and VTF fitting constants. The best fitting
parameters for the viscosity and conductivity as a function of
0
(mPa·s), 
0 a 0
(mS·cm ), E (kJ·mol-1), B/ (K), and T
(
 · is temperature dependent. Again, this behavior is already
m
well described in the literature for a large range of ILs, and
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
[
43]
[28]
according to Schreiner et al.,
a better illustration of the
series with x = 1 to 3 and y = 2 to 5 (38-56 %). In other words,
conductivity-viscosity relationship could be achieved by using a
fractional Walden rule as follows:
all investigated ILs could be considered as “good” ILs. The
threshold between the classification of “good” and “poor” ILs,
[
45]
originally proposed by Angell
is represented by the dashed
ꢘ
ꢙꢇ
ꢗ ꢀꢐ
ꢒ
diagonal line in Figure 6 and corresponds to an ionicity of 10 %.
ILs which lie below this line have a strong tendency for ion-pair
formation.
ꢑ
ꢢ
ꢘ
ꢚꢛꢜꢝꢞꢁ(ꢐ )ꢀꢛꢜꢝ (ꢗ )ꢟꢠꢒꢛꢜꢝ ꢡ ꢣꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇꢇ(ꢤ)
ꢑ
ꢞꢁ
ꢞꢁ
2.2.3. Electrochemical window
where  and W’ are an additional exponent fitting parameter and
the “Walden product” of the fractional Walden rule.
One of the reasons for the recent growing interest in ILs is the
wide electrochemical windows which may allow them to be used
as solvent-free supporting electrolytes in high-energy density
devices, including LiS batteries and electrochemical
[
46]
capacitors. Therefore, of particular interest is the relationship
between the cationic structures of the ILs and their
electrochemical windows. Cyclic voltammograms (CVs) have
been measured (Figure 6) for all investigated ILs using a 3-
electrode cell inside an Ar filled glove box, with a 0.3 cm
diameter glassy carbon disk working electrode, a fresh lithium
strip as reference electrode and a platinum wire as counter
electrode. A small quantity of Li[NTf ] salt (i.e. 20 mg of Li salt
2
per mL of IL) has been added to the IL to be used as an internal
reference.
The reduction (Ered) and oxidation (Eox) limiting potentials of the
ILs were then determined by a graphical method at the potential
value where tangent lines to the main reduction/oxidation walls
and the “flat” electroactivity domains cross. These values are
presented in the Table 3. The reduction limiting potentials
suggest that both the number and the length of the ether chains
attached on the sulfonium cation have a negligible effect on the
reduction potential of the ILs. However, such values seem to be
Figure 5. Walden plot of temperature-dependent conductivities
+
[28]
2
lower than those reported for [S1,1,4][NTf ] (0.9 V vs. Li /Li).
This difference may be explained by comparing the LUMO
and viscosities for selected sulfonium-based ILs: [S1,1,G1][NTf
), [S1,1,G2][NTf ] (), [S1,2,G1][NTf ] (), [S1,G1,G1][NTf ] () and
1,G2,G2][NTf ] (). The solid line corresponds to the Walden
2
]
(
2
2
2
energy of selected cations (average close to -4.39 eV) vs.
[
S
2
+
[
S
1,1,4
]
(-4.60 eV) as shown in Table S8 of the ESI.
plot ideal line corresponding to aqueous KCl solution. The
dashed line corresponds to an ionicity of 10 %.
Table 3. Oxidation (Eox
electrochemical windows (E) of selected [NTf
)
and reduction (Ered) limiting potentials and
-
2
] -based sulfonium ILs.
For all investigated ILs, excellent correlations have been
achieved by applying the fractional Walden rule (eq. 5) with
E
ox
E
red
E
2
-1
Cation
+
+
slopes (i.e. ) and intercepts (i.e. log(W’ / S·cm ·mol )) ranging
from (0.91 to 0.99) and from (-0.29 to -0.53), respectively. The
linear fitting parameters for each IL are shown in Table S7 in the
ESI.
(V vs. Li /Li)
(V vs. Li /Li)
(V)
+
+
+
[
[
[
S
S
S
1,1,G1
1,1,G2
1,2,G1
]
]
]
5.09
4.94
5.11
4.75
4.69
1.34
1.37
1.24
1.36
1.36
3.75
3.57
3.87
3.39
3.33
Based on parameters reported in Table S7, the ionicity of all the
five ILs range between 30 % and 50 %. Furthermore, the ionicity
seems to decrease with increasing the degree of asymmetry and
functionalization within the alkyl chain and follows the trend:
+
+
[S1,G1,G1
]
[S
1,G2,G2
]
+
+
+
[
[
S
S
1,1,G1
]
(50 %) > [S1,2,G1
]
(45 %) >> [S1,G2,G2
]
(35 %) ≈
+
+
1,G1,G1] (34 %) ≥ [S1,1,G2] (29 %). In other words, an increase
of the degree of asymmetry and functionalization on the
sulfonium cation seems to induce an increase of ion-pairing in
solution. Although, the ionicity values are lower than those
determined for the 1-ethyl-3-methylimidazolium tetrafluoroborate
[
43]
(
[C
bis{(trifluoromethyl)sulfonyl}imide ([C
ILs reported are similar than those calculated for the [S1,x,y][NTf
2
mim][BF
4
], 81 %)
or the 1-butyl-1-methylpyrrolidium
[
44]
4
mpyrr][NTf
2
], 66 %)
the
2
]
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
cations was then further examined by comparing the HOMO
energy of selected cations determined from DFT calculations as
shown in Table S8 of the ESI. From these data, it can be
observed that the HOMO energy is always localized on the
oxygen atom furthest from the sulfonium centre and seems to
decrease by increasing the degree of functionalization. For
example, HOMO energies close to -11.20; -9.97; -9.55 eV were
2 2 2
observed for the [S1,1,G1][NTf ], [S1,1,G2][NTf ], [S1,G2,G2][NTf ],
respectively. However, such energies are much lower (i.e. more
stable toward the oxidation) than those determined for each
-
conformation of the [NTf
2
] anion (e.g. -4.19; -3.97 and -3.89 eV;
see Table S8 of the ESI), as expected. In other words, all DFT
calculations done during this work (individual ions and ion pair)
seem to reveal that only the anion may participate, directly, to
the oxidation of each IL. However, stronger cation-anion
interaction may be expected for ILs presenting a stronger
tendency to form ion pairs in solution. Interestingly, by
comparing results of the ionicity and oxidation limiting potentials,
it appears than both properties seem to be correlated, as ILs
presenting lower ionicity levels, such as [S1,G1,G1][NTf
2
],
[
S
1,1,G2][NTf
2
] and [S1,G2,G2][NTf ], have also lower oxidation
2
potentials. This may be associated to the fact that both the
cation and anion have less mobility/configuration freedom than
those in [S1,1,G1][NTf ] or [S1,2,G1][NTf ]. On the one hand, strong
2 2
cation-anion interaction may indicate the possibility for the cation
to participate to the oxidation process as claimed by some
[
48]
authors, on the other hand, a low degree of freedom may also
influence the probability of finding various anion and cation
conformations in solution. Interestingly, DFT calculations of the
-
2 2
ion pair [S1,G1,G1][NTf ] suggest that the conformation cis-[NTf ]
surrounding the cation is the most stable, for example (see
Table S8 of the ESI). However, in the case of the single anion
DFT calculations, this conformation is not the most stable and
led to an increase of the anion HOMO energy close to +0.22 eV
vs. the trans-conformer. In both cases, the degree of
functionalization of the cation seems to impact, strongly, on the
oxidation potential of the ILs. This may be driven by a change on
the cation-anion interactions inducing a radical change of the
anion conformer ratio (cis vs. trans) involving a decrease of the
oxidation potential. This hypothesis could also explain why the
electrochemical windows of the selected ILs, which range from
Figure 6. Electrochemical windows of [S1,1,G1][NTf
2
]
(a),
[
[
S
S
1,1,G2][NTf
1,G2,G2][NTf
2
] (b), [S1,2,G1][NTf ] (c), [S1,G1,G1][NTf ] (d) and
2
2
2
] (e).
Furthermore, a comparison between the reduction potential of
+
[
[
S
S
1,1,G1][NTf
1,2,G1][NTf
2
] (e.g. 1.34 V vs. Li /Li and LUMO = -4.58 eV) and
+
2
] (e.g. 1.24 V vs. Li /Li and LUMO = -4.60 eV) tends
to indicate that the electrochemical stability of this IL series
increases by increasing the alkyl chain length, as already
[47]
reported in the case of several other ILs.
On the other hand, the data reported in Table 3 shows that the
length of the ether chains has an important effect on the
oxidation potential of the ILs even if they are all based on the
same anion. For example, a comparison of these data between
2
3.3 V to 3.9 V, are lower than those reported for the [S1,1,x][NTf ]
series with x = 2 to 5 (i.e. from 3.8 V to 4.2 V).
[28]
[
S
1,1,G1][NTf
2
], [S1,2,G1][NTf
2
] and [S1,1,G2][NTf
2
] clearly indicates 3. Conclusions
that the oxidation potential decreases by increasing the degree
of functionalization of the IL. A similar trend is also observed by
A novel family of cation-functionalized sulfonium ILs have been
synthesized and characterized. Different synthesis routes have
been investigated to be able to make targeted ILs in large scale
within a good yield (63-87 % yield). Firstly, thioethers were made
by following the conventional Williamson procedure under
aqueous conditions. Then, dialkyl-ether-sulfonium-based ILs can
be easily synthesized with a good yield by the alkylation of the
thioethers using either iodomethane or diethylsulfate. Similarly,
based on our investigations, alkyl-diether-sulfonium-based ILs
can only be obtained with a good yield by the alkylation of the
comparing the data for [S1,G1,G1][NTf
2 2
] vs. [S1,G2,G2][NTf ] and for
[
S
1,1,G2][NTf
2
]
vs. [S1,G2,G2][NTf ]. As the reduction limiting
2
potentials do not seem to be affected by the degree of
functionalization, a contrario of the oxidation limiting potentials, it
can be concluded that the degree of functionalization of the
cation does not impact the reduction of the ILs (which is quite
surprising) while it does influence the environment (interaction)
-
of the [NTf
2
] anion and thus its’ oxidative stability. The impact of
the degree of functionalization on the oxidation potential of the
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
thiodiethers using either iodomethane. These thiodiethers were
obtained by reacting sodium sulfide with 2 equivalents of the
corresponding bromogylme. In each case, anion exchange was
(ASTM Oil Standard S600 of CANNON, 1053 mPa·s at 298.15
K) and ultra-pure water were used to calibrate the viscometer.
Based on these measurements, the accuracy of reported
viscosity measurements is close to ± 1 %.
2
achieved by a simple metathesis reaction with Li[NTf ] salt.
These ILs exhibit good thermal stability, low melting points, and
good transport properties. As expected, the structure of the
cation affects strongly all investigated properties. Both the
density and conductivity decrease by increasing the degree of
functionalization, while more complex relationships were
observed in the case of the viscosity. Furthermore, according to
the Walden rule, all investigated ILs can be classified as ‘good’
ionic liquids with ionicity ranging from 30 % to 50 %. The ionicity
seems to be strongly affected by the degree of asymmetry and
Dynamic thermogravimetric analysis (TGA) of each IL was
determined using a TGA Q5000 (TA Instruments) under nitrogen
flow with a heating rate and terminal temperature set at 5
−1
K·min
and 773.15 K, respectively. The decomposition
, is taken when the samples had lost 5 %
temperature onset, T
d
of their initial masses. Reported thermal properties are given
with accuracy close to ± 1 K.
Thermal phase transitions of each IL were recorded using
differential scanning calorimetry (DSC) traces on a DSC Q2000
of functionalization on the cation structure. The [S1,1,G1][NTf
the highest ionicity (50 %), followed by the [S1,2,G1][NTf ] (45 %),
while lower values (29-35 %) have been obtained for
]. Interestingly, a
2
] has
(
TA Instruments). Hermetically sealed aluminum pans containing
2
the respective IL sample were prepared inside the Ar-filled glove
box for DSC analysis. A sample of average weight of ~ 5 mg
was hermetically sealed in an aluminum pan, and then heated
2 2 2
[S1,G1,G1][NTf ], [S1,1,G2][NTf ] and [S1,G2,G2][NTf
similar trend was observed for the electrochemical windows of
these ILs with a strong impact of the degree of functionalization
−
1
and cooled at a rate of 5 K·min from 183.15 K to 273.15 K
under a flow of nitrogen. The glass transition temperature (T
onset of the heat capacity change), crystallization temperature
, onset of the exothermic peak), and melting point (T , onset
g
,
of the cation on this property. This impact may be related to
-
2
strong interactions between functionalized cation and the [NTf ]
(
T
c
m
anion leading to a slight decrease of the oxidation limiting
potential of these ILs. However, these functionalized sulfonium
ILs show quite large electrochemical windows higher than 3.3 V.
In other words, the results obtained during this work indicate that
these ILs could be applied in electrochemical energy storage
of the endothermic peak) were recorded on the first or second
heating scans with accuracy close to ± 0.25 K.
Conductivity measurements were performed using a sensION+
EC71 benchtop meter with a 3-pole platinum sensION+ 5070
conductivity probe with an in-built Pt1000 temperature probe
devices. In particular, the application of this class of ether-
-
(
Hach Lange). The conductivity probe was calibrated using
functionalized sulfonium [NTf
2
] -based ILs in electrochemical
-1
aqueous KCl standard conductivity solutions (147 μS.cm , 1413
double layer capacitors is currently being investigated.
-1
-1
μS.cm , and 12.88 mS.cm at 298.15 K). The immersion and
sealing of the conductivity probe in the liquid sample was carried
out in an Ar-filled glovebox. The conductivity probe
4. Experimental Section
(
disconnected from the meter) was immersed in the liquid
sample inside a glass sample tube with a small magnetic stirrer.
The sample was sealed using an O-ring seal and parafilm. The
conductivity of the sample was then recorded with stirring as a
function of temperature (using the temperature reading built into
the conductivity probe). The temperature of the sample was
varied from 263.15 K to 353.15 K using a small oil bath and a
hot-plate with a thermocouple control. The temperature and
conductivity of the sample was recorded when the values were
stable for ca. 1 min with accuracies close to 0.05 K and 1 %,
respectively.
4
.1. Materials used during the ILs synthesis
Dimethylsulfide (98 %), sodium thiomethoxide (21 wt% in H
2
O),
sodium sulfide nonahydrate (98 %) and 1-bromo-2-(2-
methoxyethoxy)ethane (95 %) were purchased from Sigma-
Alrich. 2-Bromoethyl methyl ether (95 %) was purchased from
Fluorochem. Lithium bis{(trifluoromethyl)sulfonyl}imide (Li[NTf ])
2
was purchased from 3M. All solvents purchased from MACRON
were of HPLC grade and used as received.
4
.2. Methods used during the ILs characterization
Prior to any physiochemical, thermophysical
electrochemical measurement all the ILs were dried under high
and
All electrochemical measurements were performed using a
Versatile multichannel potentiostat (Biologic S.A) inside an Ar-
filled glovebox. The measurements have been conducted at a
-3
vacuum (2 x 10 mbar) for 48 h at 343.15 K. The water content
in ILs was analyzed by means of a coulometric Karl-Fischer
titration using an 899 Coulometer (Metrohm) with an accuracy
better than 10 ppm.
-1
scan rate of 2 mV·s in a 3-electrode cell using a 0.3 cm
diameter glassy carbon as the working electrode, a fresh lithium
metal strip as the reference, and a platinum wire as the counter
electrode. The electrolyte consisted of ca. 1 mL of pure IL in
Density measurements were performed using a DM40 (Mettler
Toledo) oscillating tube densitometer in the range of 293.15 -
2
which a small quantity of Li[NTf ] (approx. 20 mg) was dissolved
+
-4
-3
to introduce a Li /Li reference system.
363.15 K (± 0.01 K) within an accuracy close to ± 10 g·cm .
Prior to any measurements, the instrument was cleaned with
acetone and dried with dehumidified air.
HOMO and LUMO energies of each species have been
[
49]
determined by using the Turbomole 7.0 program package.
Prior to visualization of these orbitals using TmoleX (version
.1.1), the structure of each ion involved was optimized, with a
The viscosity of the ILs was measured using a Bohlin Gemini
Rotonetic Drive 2 cone and plate rheometer from 267 K to 370 K
4
−
8
convergence criterion of 10 Hartree in the gas phase, by using
(
± 0.01 K) at atmospheric pressure. The viscosity standard
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
DFT calculations combining the Resolution of Identity (RI)
4
layer consisting of the sulfonium ethylsulfate, [S1,2,G1][EtSO ],
[
50]
approximation
within the Turbomole 7.0 program package
was removed. The resulting ethyl sulfate IL was dissolved in 100
mL of ultrapure water, before being washed successively with
100 mL fractions of ethyl acetate (3 times) and diethyl ether (3
times) to remove traces of thioether. The resulting ethyl sulfate
[51]
utilizing the B3LYP functional with the def-TZVP basis set.
Each resultant optimized structure was then used as an input for
the generation of the conformers of each species using the
COSMOconfX program (version 4.0). The orbitals of each
conformer were then determined using single point energy
calculations (DFT/B3LYP/def-TZVP + RI approximation) within
Turbomole.
IL was subjected to metathesis with Li[NTf
procedure to that described above.
2
] in an identical
4.3.4. Synthesis of the thiodiethers 2a and 2b
Sodium sulfide nonahydrate of (82.459 g, 0.336 mol, 1 eq.) was
dissolved in 100 mL of ultrapure water. The flask was covered
by aluminum foil and immersed into an ice bath, before 98.461 g
of bromoether (0.673 mol, 2 eq.) was added dropwise over a
period of 2 h. The mixture was then stirred and allowed to return
slowly to room temperature for 48 h, yielding two phases. The
organic phase was removed and the aqueous phase was
extracted with 50 mL fractions of diethyl ether (3 times) and the
combined organic phase and extracts were gathered in a round-
bottom flask. The diethyl ether was removed under vacuum to
leave the crude thioethers 2a and 2b. These were deemed pure
4
.3. General synthesis of the sulfonium-based ILs
4.3.1. Synthesis of the thioethers 1a and 1b
To a flask containing a 21 wt% aqueous solution of sodium
thiomethoxide (182.942 g, 0.548 mol, 1.1 eq.) was slowly added
over 2 h the corresponding bromoether (0.498 mol, 1 eq.) The
reaction mixture was covered by aluminum foil and immersed in
an ice bath. After complete addition of the bromoether the
mixture was stirred and allowed to return slowly to room
temperature for approximately 15 h. To this was added 50 mL of
diethyl ether to dissolve and extract the methylthioether
intermediates, 1a and 1b. The aqueous phase was further
extracted with portions of diethyl ether (2 x 25 mL) and all of the
organic extracts were gathered in a round bottom flask covered
by aluminum foil and immersed into an ice bath. The diethyl
ether was removed under vacuum to leave the crude thioethers
1
enough by H-NMR to continue with the synthesis.
1
Bis (2-methoxyethyl)sulphide 2a: H NMR (300 MHz, CDCl
3
): δ
(ppm) = 3.57 (t, J = 6.6 Hz, 4H), 3.37 (s, 6H), 2.76 (t, J = 6.6 Hz,
4H).
1
Bis (2-(2-methoxyethoxy)ethyl) sulphide 2b: H NMR (300 MHz,
1
which were characterized by H-NMR and found to be of a high
enough purity to be used for the subsequent synthesis steps.
CDCl
3
): δ (ppm) = 3.69 – 3.59 (m, 8H), 3.54 (s,4H), 3.39 (s, 6H),
.77 (t, J = 7.0 Hz, 4H)
.3.5. Synthesis of alkyldiether sulfonium-based ILs
2
1
1- methylthio-2-methoxy ethane 1a: H-NMR (300 MHz, CDCl
3
):
4
δ (ppm) = 3.49 (s, 2H), 3.29 (s, 3H), 2.50 (d, J = 62.8 Hz, 2H),
2 2
[S1,G1,G1][NTf ] and [S1,G2,G2][NTf ]
2
.06 (s, 3H).
-methylthio-2-(2-methoxyethoxy)ethane 1b: H-NMR (300 MHz,
): δ (ppm) = 3.64 – 3.45 (m, 6H), 3.31 (s, 3H), 2.62 (t, J =
.9 Hz, 2H), 2.07 (s, 3H).
.3.2. Synthesis of dialkylether sulfonium-based ILs
Iodomethane (72.420 g, 0.505 mol, 1.5 eq.) was added slowly
dropwise over a period of 2 h to the respective thioether (0.49
mol, 1.0 eq.) in ultrapure water (100 mL) and the biphasic
mixture was stirred at room temperature for 15 h. After this the
resulting aqueous solution was washed successively with 100
mL fractions of ethyl acetate (3 times) and diethyl ether (3 times)
to remove excess iodomethane and traces of thioether. The
resulting sulfonium iodide solution was then stirred with a
1
1
CDCl
6
3
4
2 2 2
[S1,1,G1][NTf ], [S1,1,G2][NTf ] and [S1,2,G1][NTf ]
Iodomethane (107.215 g, 0.748 mol, 1.5 eq.) was added slowly
dropwise over a period of 2 h to the thioether (0.49 mol, 1.0 eq.)
in ultrapure water (100 mL) and the biphasic mixture was stirred
at room temperature for 15 h. After this the resulting aqueous
solution was washed successively with 100 mL fractions of ethyl
acetate (3 times) and diethyl ether (3 times) to remove excess
iodomethane and traces of thioether. The resulting sulfonium
2
solution of Li[NTf ] (103.534 g, 0.353 mol, 1.05 eq.) in 150 mL of
ultrapure water for 15 h at room temperature in a flask covered
by aluminum foil. Thereafter, 100 mL of dichloromethane was
added to dissolve the IL, which is then washed 15 times with 20
mL fractions of ultrapure water. The absence of iodide traces
was verified with a silver nitrate test. Dichloromethane was then
removed on a rotary evaporator.
2
iodide solution was then stirred with a solution of Li[NTf ]
(
153.805 g, 0.525 mol, 1.05 eq.) in 150 mL of ultrapure water for
15 h at room temperature in a flask covered by aluminum foil.
4.4. Chemical characterization of the sulfonium-based ILs
Thereafter, 100 mL of dichloromethane was added to dissolve
the IL, which was then washed 15 times with 20 mL fractions of
ultrapure water. The absence of iodide traces was verified with a
silver nitrate test. Dichloromethane was then removed on a
rotary evaporator and the IL was further dried under vacuum
1
13
H- and C-NMR spectra were recorded at 293.15 K on a
Bruker Avance DPX spectrometer at 300 MHz and 75 MHz,
respectively and are reported as Figures S1 to S5 of the ESI. To
avoid further contamination with moisture from the atmosphere,
the ILs were stored in a glovebox under an Ar atmosphere with a
moisture content below 3 ppm. Microanalysis and lithium content
were performed by Analytical Services at Queen’s University,
Belfast.
-3
(
10 mbar) at 353.15 K during 3 days.
4
.3.3. Synthesis of dialkylether sulfonium-based IL [S1,2,G1][NTf ]
2
Diethyl sulfate (77.09 g, 0.5 mol, 1.0 eq.) was added slowly
dropwise over a period of 2 h to the thioether 1a (0.49 mol, 1.0
eq.) in a solution of ethyl acetate (200 mL) and the mixture was
stirred at room temperature for 15 h. After this a viscous lower
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ChemPhysChem
10.1002/cphc.201600882
ARTICLE
4
.4.1. Dimethyl(2-methoxyethyl)sulfonium bis{(trifluoromethyl)- Acknowledgements
sulfonyl}imide [S1,1,G1][NTf
2
]
The authors would like to gratefully acknowledge the funding
from the CEA le Ripault.
Following the synthesis procedure, the title compound was
1
obtained as a colorless liquid, 81 % yield. H-NMR (300 MHz, d
6
-
DMSO): δ (ppm) = 2.88 (s, 6H), 3.31 (s, 3H), 3.53 (t, J= 5.5 Hz,
AN, PG, CH and JJ would like also to gratefully acknowledge the
funding from EPSRC (EP/L505262/1) and Innovate UK for the
Practical Lithium-Air Batteries project (project number: 101577).
Supporting data are openly available on Queen’s University
Research Portal: http://pure.qub.ac.uk/portal/en/datasets.
13
2
H), 3.76 (t, J= 5.7 Hz, 2H). C-NMR (75 MHz, d
6
-DMSO): δ
(
ppm) = 24.90, 42.75, 58.32, 65.70 (cation); 119.64 (q, JCF
3
2
1
20.25 Hz) (anion). CHNS calcd.: C, 20.95; H, 3.26; N, 3.49; S,
3.97; Found: C, 21.00; H, 3.26; N, 3.37; S, 24.00. H
6 ppm. Li content: 16 ppm.
2
O content:
4.4.2.
Dimethyl[2-(2-methoxyethoxy)ethyl]sulfonium
bis-
Keywords: Ionic Liquids • Sulfonium • Ether • Electrochemical •
{
(trifluoromethyl)sulfonyl}imide [S1,1,G2][NTf
2
]
Physical and Transport Properties
Following the synthesis procedure, the title compound was
1
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6
-
DMSO): δ (ppm) = 2.89 (s, 6H), 3.26 (s, 3H), 3.46 (m, 2H), 3.54
13
(
(
6
t, J= 5.1 Hz, 2H), 3.60 (m, 2H), 3.86 (t, J= 5.1 Hz, 2H). C-NMR
75 MHz, d -DMSO): δ (ppm) = 24.80, 42.83, 58.03, 64.30,
9.50, 71.00 (cation); 119.61 (q, JCF 318.75 Hz) (anion). CHNS
calcd.: C, 24.27; H, 3.85; N, 3.14; S, 21.60; Found: C, 25.38; H,
3692.
6
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2
O content: 26 ppm. Li content: 13 ppm.
4.4.3. Ethylmethyl(2-methoxyethyl)sulfonium
bis{(trifluoro-
methyl)sulfonyl}imide [S1,2,G1][NTf
2
]
13280-13285.
Following the synthesis procedure, the title compound was
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1
obtained as a colorless liquid, 87 % yield. H-NMR (300 MHz, d
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-
[
[
[
5]
6]
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13
3
(
6
.44 (s + m, 5H), 3.56 (m, 2H), 3.77 (t, J= 5.4 Hz, 2H). C-NMR
75 MHz, d -DMSO): δ (ppm) = 8.25, 21.72, 35.52, 40.53, 58.26,
5.65 (cation); 119.51 (q, JCF 320.25 Hz) (anion). CHNS calcd.:
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N, 3.93; S, 23.08. H O content: 28 ppm. Li content: 18 ppm.
.4.4. Di(2-methoxyethyl)methylsulfonium bis{(trifluoromethyl)-
sulfonyl}imide [S1,G1,G1][NTf
Following the synthesis procedure, the title compound was
2
2010, 195, 845-852.
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obtained as a colorless liquid, 68 % yield. H-NMR (300 MHz, d
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-
methanol): δ (ppm) = 3.00 (s, 3H), 3.44 (s,6H), 3.57 (t, J= 5.7 Hz,
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.4.5. Di[2-(2-Methoxyethoxy)ethyl]methyl
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.70 (m, 6H), 4.00 (t, J= 5.2 Hz, 4H). C-NMR (75 MHz, d
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ARTICLE
Entry for the Table of Contents
ARTICLE
Erwan Coadou,* Peter Goodrich, Alex R.
Neale, Laure Timperman, Chistopher
Hardacre, Johan Jacquemin,* Mérièm
Anouti
Synthesis and Thermophysical
Properties of Ether Functionalized
Sulfonium Ionic Liquids as Potential
Electrolytes for Electrochemical
Applications
During this work, novel ether functionalized sulfonium
bis{(trifluoromethyl)sulfonyl}imide ILs were synthesized and deeply characterized.
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